The gene encoding for four different ribosomal proteins, designated emt A, emt B, emt C, and brur and defined by various mutants isolated in this laboratory, will be assigned to specific Chinese hamster and human chromosomes. These experiments will involve cytogenetic and biochemical analyses on appropriate inter- and intraspecific cell hybrids and segregants derived from them. In addition, the effect of a large difference in gene dosage for different of the genes encoding for various ribosomal proteins and the biosynthesis of ribosomes and the normally coordinate expression of this group of genes will be examined. Biochemical and genetic characterization of Chinese hamster tRNA synthetase mutants which have received the mouse or human genes for asparyl- and leucyl-tRNA synthetase, via transformation with total genomic DNA, will be continued. The goal of this project is to clone the genes encoding for these two aminoacyl-tRNA synthetases.